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Efficacy of ketamine for major depressive episodes at 2, 4, and 6-weeks post-treatment: A meta-analysis

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Major depressive episodes are severe mood episodes which occur both in major depressive disorder and bipolar I and II disorder. Major depressive episodes are characterized by debilitating symptoms that often persist and interfere with typical daily functioning. Various treatments exist for major depressive episodes; however, most primary pharmacologic treatments may take weeks to months to provide relief from depressive symptoms. Ketamine is a demonstrated treatment for major depressive episodes, as relief from depressive symptoms can occur rapidly following treatment.


Prior meta-analyses have been conducted to analyze the effectiveness of ketamine for the treatment of major depressive episodes, but at the time of this writing, no meta-analysis had been conducted to observe ketamine treatment efficacy beyond 2 weeks.


The present meta-analysis evaluated the efficacy of ketamine for the treatment of major depressive episodes; observations of depressive episode severity were analyzed at 2, 4, and 6-weeks post-treatment.


The present meta-analysis observed large effects at 2 weeks (g = −1.28), 4 weeks, (g = −1.28), and 6 weeks (g = −1.36) post-treatment.


The results from the present meta-analysis indicate that ketamine can be an effective pharmacologic intervention for major depressive episodes, with treatment effects lasting up to 6 weeks post-ketamine administration, which has many positive implications for treatment.

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The datasets generated during and/or analyzed during the current study are available in the OSF repository,


*References marked with an asterisk indicate studies included in the meta-analysis. +References marked with a plus symbol indicate studies that were imputed and reported in the Supplement

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Correspondence to Ashley A. Conley.

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Conley, A.A., Norwood, A.E.Q., Hatvany, T.C. et al. Efficacy of ketamine for major depressive episodes at 2, 4, and 6-weeks post-treatment: A meta-analysis. Psychopharmacology 238, 1737–1752 (2021).

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